Underwater sound transducer



May 8, 1956 F. F. BUNDY 2,745,084

UNDERWATER SOUND TRANSDUCER Filed Aug. 29, 1945 FIG. 4.

INVENTOR FRANCIS P. BUNDY BY LW ATTOR N EY United States UNDERWATER soUND TRANSDUCER 5 Application August 29, 1945, Serial No. 613,352

9 Claims. (Cl. 34011) This invention relates to underwater sound transducers 15 and more particularly to transducers of the magetostrictive type.

Transducers as constructed heretofore usually comprise an oscillator made of consolidated thin laminations and having slots of uniform width arranged perpendicular to the active vibrating face of the oscillator. The portions of the oscillator between the slots constitute magnetostrictive legs of uniform width which are energized by coils disposed in the slots. Permanent magnets between the legs and substantially filling the slots laterally thereof, provide a polarizing flux which enters the legs substantially perpendicular thereto at their centers. Since the point of maximum strain in a leg when it is vibrating is at the node, this point also, in a leg of uniform width is at the center of the leg. Consequently, the magnetostrictive effect of the flux is impaired because the direction of flow of the flux at the point of maximum strain departs from the effective direction of the magneto-strictive force and particle movement in the leg, which is lengthwise of the leg.

Thus, a transducer of this type has a low eifective electro-mechanical coupling coefficient, and hence, a low efficiency.

Under conditions conducive to high echo strength, a transducer of this type may be satisfactory; but one of 40 greater efliciency is required for applications in which the echo strength may be expected to be low and a correspondingly high transmitting power is necessary.

In view of the foregoing, it is a primary object of the invention to provide an improved magneto-strictive transducer of higher efiiciency than has been attained in this type of equipment heretofore.

To this end, and in accordance with one feature of the invention, the magneto-strictive legs of the illustrated oscillator are so shaped and arranged as to cause the flux therein resulting from a polarizing field to flow, at the point of maximum strain, in the direction of the magnetostrictive force and particle movement in the legs, whereby a maximum magneto-striction is caused by any given amount of flux.

In the illustrated oscillator, the polarizing field is provided by permanent magnets disposed between its magneto-strictive legs. Furthermore, the portions of the legs which are coextensive with the magnets have lobes which make them relatively stiff and massive as compared with the remaining length of the legs which is relatively elastic. This construction, in which invention is to be recognized, gives rise to two conditions which mutually effect at the point of maximum strain and becomes parallel to the direction of strain at that area. Hence, except for unavoidable losses arising from eddy currents, heat, and the like, the transfer of energy between its electrical and mechanical or acoustic phases, in the operation of the illustrated transducer, is as complete as possible.

With the above and other objects and features in view, the invention will now be described with reference to the accompanying drawings, which illustrate preferred embodiments of the invention, and will be pointed out in the claims.

In the drawings:

Fig. 1 is a diagrammatical view of an illustrative magneto-strictive oscillator for a transducer embodying the invention;

Fig. 2 is a diagrammatical view illustrating certain electrical features which result from the oscillator construction provided by the invention;

Fig. 3 is a plan view of a lamination for an oscillator like that of Fig. 1 but cylindrical in form; and,

Fig. 4 is a diagrammatical plan view of a modification of the oscillator of Fig. 3 in which is employed a circular arrangement of segmental magneto-strictive units.

The oscillator shown in Fig. 1 comprises a stack of nickel laminations of any suitable height, as for example 2" to 3" the laminations being alined, and consolidated by an adhesive and insulating substance. Each lamination has a series of perforations of unequal Width which result in the formation of opposed flanges 10 and 12, and integral therewith a series of legs each of which has a relatively massive lobed portion 14 intermediate between relatively narrow elastic portions 16.

In the larger parts of the slots between the elastic legportions are placed coils 18 (Fig. 2) by which the transducer is energized. In the interest of clarity the coils have been omitted from Fig. 1, but their orientation has been indicated by positive and negative signs. Each coil comprises about twenty-five turns of wire and is generally rectangular in form.

Inside each coil and between the lobed leg-portions 14 are disposed one or two polarizing magnets 20 which are substantially coextensive with the leg-portions 14. Successive magnets are arranged with their like poles facing each other across the intervening leg.

In the usual type of prior transducer having legs of uniform width, the point of maximum strain, which is at the node of the vibratory member, is at the center of each leg. Furthermore, with magnets and coils disposed as above described with respect to a leg of uniform width, it is apparent that since the flux from the magnets enter the central portion of the legs substantially at right angles thereto, the direction of the flux flow at the point of maximum strain is perpendicular, or nearly so, to the direction of the magneto-strictive stress. Accordingly, a transducer so constructed has a low effective electro-mechanical coupling coeflicient and hence a low efiiciency. For example, in a typical transducer having legs of uniform width, the coupling coefficient has a theoretical value of 0.082 and a measured value of 0.0304, for a lamination material having a maximum coupling coefiicient-of 0.223. The reason for the discrepancy and the low actual coupling is essentially in the relatively ineffectual direction of the flux path provided by the legs of uniform width at the point of maximum strain.

The above mentioned condition is avoided in the illustrated oscillator by the provision of the massive lobed, leg-portions 14, as will now be explained with reference to Fig. 2. .Such thickening of the legs adjacent to the magnets renders those portions of the legs relatively stiff, with the result that the point of maximum strain (stress per unit area) occurs in the narrow relatively elastic The'lobed leg portions 14 further provide a path for r the flux which has its junction between the polarizing magnet and the leg at a location where the leg is relatively stifi andftherefore of relatively little use for magneto-s triction. I a

Thus, the point of maximum strain and the path of the flux flow have been brought into the optimum rela tion from the standpoint of obtaining the maximum magneto-strictive eflect from a given amount of flux. The efliciency'of 'a transducer constructed in accordance with the invention as compared with one having legs between said legs and spaced from said flange, and energizing coils positioned aboutthe portion of said legs between said magnets and flange, said legshaving lobes substantially coextensive with said magnets providing rela-' V tively massive leg-portions adjacent to said magnets whereby the points of maximum strain in said legsare estab' lished at areaswhere the flux in said legs flows in the effective :direction ofthe magneto-strictive force.

2. An underwater sound transducer comprising a laminated oscillator of magneto-strictive material having a rsound propagating flange, spacedlegs extending from said flange, portions of said legs remote from said .flange having lobes providing stilt leg-portions which are conof uniform width is approximately quadrupled, the effeetive coupling coefliciency being about 0.164.

' This increased efliciency of the illustrated transducer is also derived partly from an improvement in the flow of "flux between the magnets and thelobed leg-portions. To the extent that the lobed portions of the legs are widened, the distance between them, and hence the reluctance of the path of A. C. flux from the windings is reduced. Similarly, since the magnets necessarily have a high resistivity, the narrower their lateral dimension, the lower'will be the reluctance of the path of the A. C. flux in the magnets. For best results, the width of the magnets should be between A and of the length of the flux path along two adjacent legs and the flange connecting them.

Ina transducer of the type shown in Fig.1, both flanges 10 and '12 are oscillating members capable of initiating sound in directions perpendicular to their faces. 7

However, if only one flange, such .as 10 for example, is desired to be-utilized as a sound propagating flange, the transducer may be mounted with its back flange 12 against a pressure release material with low acoustic resistance (such as air'cell neoprene orcorprene) to prevent radiation from it.

Where sound radiation is to be effected throughout an angular area, with the above described advantages provided by the invention, an'oscillator of the cylindrical form illustrated in Fig. 3 may be employed. This figure represents a type of lamination which is perforated to provide legs having stiff lobed portions 24, and elastic portions 26, and also a sound propagating flange 28. A section'including such legs and the flangemay be of any desired size, depending upon the angular area to be covered. Only a small sector has been shown in Fig. 3 for ease of illustration.

In the modification shown in Fig. 4, the oscillator comprises a series of segmental units arranged, as a whole, in an annular formation. The .-laminations of each unit have a sound propagating flange from which nected to said flangezby relatively elasticleg-portions whereby the point of maximum strain is established within said relatively elastic portion near the junction of said elastic and stiff leg portions, polarizing magnets disposed between the lobes of said legs, and energizing coils positioned about the relativelyelastic portion of said legs. 7

3. An underwater sound transducer comprising a laminated oscillator ofimagneto-strictive material having 'a sound propagating flange, spaced legs having relatively,

elastic portions extending from said flange, energizing coils positionedabout said elastic leg-portions, polarizing magnets disposed between said legs, theportion of said legs adjacent to said magnets being stitt compared to said elastic portions whereby the points of maximum strain are spaced from said magnets in said elastic leg-portions where substantially all the flux from said magnets flows in the direction of particle movement.

4. An underwater sound transducer comprising a laminated oscillator, of magneto-strictive material having a sound propagating flange, spaced legs integral with and extending from said flange, each of said legs having a lobed, relatively stiff intermediate portion between recessed, relatively elastic'portions, polarizing-magnets disposed between the lobed portions of successive legs, and

energizing coils disposedin the' slots between there-v cessed elastic portions of successive legs.

5. An underwater sound transducer comprising a laminated oscillator of magneto-strictive material having a sound propagating flange, spacedlegs extending from" 7 said flange, each of said legs having a relatively elastic portion integral withsaid flange and a lobed relatively stiff terminal portion integral with said elastic portion,

- in said elastic portion in the direction of particle movement therein. V

6. A sound transducer comprising, a plurality of flat annularlarninations of magneto-strictive material packed together toform a core having a plurality of spaced radial slots cut therein to form, a plurality of spaced legs.

extending substantially across said annular laminations, each of .said' legshaving a lobed portion intermediate relatively elastic portions, polarizing magnets disposed extend two legs each having a terminal, relatively stiff, i

lobed portion 32 and a relatively narrow and elastic portion 34. Magnets 36 are disposed between the lobed leg-portion 32 of the units and coils 38 are associated with the elastic leg-portion 34. A f

' It is noted that the relation between the point of maximum strain, which is along the line MS, and theflux flow is the same in the transducers represented by Figs. 3 and 4 as in the type of transducer shown-in Figs. 1

and 2. 1

of magnetostrictive material having a sound propagat -ing flange, spaced legs integral with and extending from said flange, each of said legs having a lobed intermedifate portion between relatively elastic portions, polariz between the lobes of successive legs, and energizing coils positionedabout the elastic portions of said legs.

7. A sound transducer comprising, a laminated core ing magnets disposed between the lobed portions of successive legs, and energizing coils'positioned about the elastic portions of said legs.

perforationsof nonuniform width therethrough forming a pair of opposed flanges having a series'of legs integral therewith and extending therebetween, each of said legs of successive legs with like poles facing each other across the intervening leg, a plurality of current carrying coils disposed between the narrow portions of said legs and surrounding said magnets, said lobed portions together with said arrangement of magnets and coils providing a flow of flux in said narrow portions of said legs which is parallel to the effective magnetic force in said narrow portions at the point of maximum strain in said narrow portions.

9. A transducer comprising a stack of laminations of magneto-strictive material having a series of spaced perforations therethrough forming a flange having a series of legs integral therewith, each of said legs being of nonuniform width along its length having a narrow portion adjacent said flange and a wider lobed portion remote from said flange, a plurality of polarizing permanent magnets disposed between the lobed portions of successive legs, a like plurality of current conducting coils positioned in the perforations between the narrow portions References Cited in the file of this patent UNITED STATES PATENTS 1,882,401 Pierce Oct. 11, 1932 1,966,446 Hayes July 17, 1934 2,088,324 John July 27, 1937 2,190,666 Kallmeyer Feb. 20, 1940 2,279,322 John Apr. 14, 1942 2,411,911 Turner Dec. 3, 1946 2,452,085 Turner Oct. 26, 1948 

2. AN UNDERWATER SOUND TRANSDUCER COMPRISING A LAMINATED OSCILLATOR OF MAGNETO-STRICTIVE MATERIAL HAVING A SOUND PROPAGATING FLANGE, SPACED LEGS EXTENDING FROM SAID FLANGE, PORTIONS OF SAID LEGS REMOTE FROM SAID FLANGE HAVING LOBES PROVIDING STIFF LEG-PORTIONS WHICH ARE CONNECTED TO SAID FLANGE BY RELATIVELY ELASTIC LEG-PORTIONS WHEREBY THE POINT OF MAXIMUM STRAIN IS ESTABLISHED WITHIN SAID RELATIVELY ELASTIC PORTION NEAR THE JUNCTION OF SAID ELASTIC AND STIFF LEG PORTIONS, POLARIZING MAGNETS DISPOSED BETWEEN THE LOBES OF SAID LEGS, AND ENERGIZING COILS POSITIONED ABOUT THE RELATIVELY ELASTIC PORTION OF SAID LEGS. 